1. Field of the invention
This invention relates to an improved method of dyeing textile materials of polycapronamide or Nylon 6 (a polymer of caprolactame). More specifically, the invention concerns the dyeing of Nylon 6 short fiber or staple with acidic dyestuffs, in particular for dyeing carpets from such materials, and even more particularly for dyeing with a method known as "winch".
As a rule, polyamide staples of Nylon 6 have a fairly high dye pick-up rate, which can be ascertained through a standard test to be explained hereinafter. Should a particular Nylon 6 staple fail to provide satisfactory results when so tested, the results of an application of this invention to that particular staple may be disappointing, and apt to be in all cases below optimum. Therefore, the invention is concerned, in a particularly preferred way, with those Nylon 6 staples which meet the requirements of the test presently described, and to articles of manufacture--in particular carpets--formed from such staples.
The test in question is as follows.
5 g of the fiber to be tested are weighed and a dyeing step conducted in the following conditions:
the dyeing bath is prepared at 20.degree. C. with: C.I. acid blue 280 as applied at the standard intensity of 1/1 (e.g., 2% Blue Nylosan N-5GL 200% --Sandoz) PA0 pH=6 buffered (e.g., about 2.5 g/l monosodic phosphate and 0.5 g/l bisodic phosphate) PA0 R.B.=1:60 with the use of soft water. PA0 the material to be dyed is introduced into the dyeing bath so prepared, stirred continuously, and held there for 10 minutes at 20.degree. C., thereafter the dyeing bath is heated slowly and gradually for 40 minutes (heating thermal gradient of 1.degree. C./min) to 60.degree. C. and held there for 60 minutes at a constant temperature of 60.degree. C. PA0 (a) use of at least two discrete acidic dye combinations, which combinations have different kinetic dyeing characteristics in the sense which will be specified hereinafter; PA0 (b) maintenance of an alkaline pH essentially throughout the dyeing method, but at tapering values, in the extreme, down to neutral, preferably from an initial range of 10 to 8.5 to a final range of 9.5 to 7; PA0 (c) use of exclusively anionic dyeing aids; PA0 (d) maximum temperatures up to 60.degree. C., preferably up to 40.degree. C.
R.B. stands for Bath Ratio, i.e. the ratio of the amount in g of material to be dyed to the amount in cc of the dyeing bath (e.g., R.B.=1:60--5 g fiber and 300 cc dyeing bath);
Those fibers which respond satisfactorily are all those fibers which, when subjected to the test described above, provide almost complete exhaustion of the dyeing bath, that is at a final dye concentration in the spent dyeing bath not exceeding 10% of its initial concentration.
Throughout the description which follows, we will make specific reference to the dyeing of carpets with the cited winch method, without this being directed to restrict the invention scope but rather understood to illustrate a typical and particularly preferred embodiment thereof and the field of application where the invention is particularly useful.
2. Prior Art
Dyeing the materials in question has met, in the historical development of the art, with various difficulties. On the one side, dyeing faults are easily encountered, such as striping, which occurs when dyeing with the winch method, also called "thrashing". On the other side, dyeing is often uneven, probably as a result of dyeing being carried out industrially on fabrics of great height, and of it being generally impossible to maintain strictly uniform conditions throughout the dyeing device. Further, the dyeing processes currently employed in the art are expensive from the standpoint of energy consumption, because they are generally carried out at temperatures of up to 100.degree. C. and above. Moreover, of course, also the dyeing of the aforesaid materials poses some problems which may be regarded as affecting the dyeing field in general, such as full exhaustion of the baths, the use of readily available dyes of relatively low cost, the achievement of desired color effects, and so forth.
A considerable advance in the specific field has been made with our copending Italian Patent Application No. 20782 A/80, wherein a dyeing method is disclosed which affords the possibility of operating at much lower temperatures than previously possible, e.g. of about 60.degree. C. In carrying out the method, use is made of conventional acidic dye terns, the tern components being required to show--in accordance with what is universally regarded as necessary in the art--comparable characteristics of absorption and migration into the fiber, such that they can be combined with the fiber to a uniform degree to provide the desired final color, resulting from the combination of the elementary dye colors.
U.S. Pat. No. 3,980,428 discloses a dyeing process for polyamides, which in some cases may be carried out at a low temperature of down to 20.degree. C. in the presence of a lactone which converts the solution pH from basic into acid (pH=5-6). While said patent specifies duration times of 3 to 48 hours for the dye fixing, actually a significant dyeing can only be obtained with the longest durations, and in all cases the process cannot be applied industrially owing to faults and irregularities in the resulting coloring, poor exhaustion of the dye, and so forth; and in actual practice, the Applicant is not aware of its having enjoyed industrial application.